It is known to provide a mechanism for centering and clamping workpieces having circular cross sections, an example of which is found in Swiss Pat. No. 352,542. As shown therein, each clamping part has a surface which fits against a surface of another clamping part, one of the clamping parts being guided glidingly on a surface lying transversely to the direction of movement of the other part, and wherein the adjustment of one clamping part is accomplished by means of a spindle. When workpieces with varying diameters are to be clamped in succession, the clamping parts must be adjusted by means of the spindle, a time consuming process.
It is particularly disadvantageous in this mechanism, as well as in clamping arrangements known as pipe vises (for example German Utility Model No. 1,131,874 or British Pat. No. 775,111), that the workpiece is held peripherally only at three or four points, and that high surface pressures, occuring as a result of the relatively small line contact existing at the contact points results in considerable surface deformation of the workpieces, especially when the workpieces are pipes made of plastic.
This disadvantage can be overcome to a degree by broadening the surface contact of the clamping jaws, thereby decreasing the unit surface pressure, but as a result of this change, the range of the clamping apparatus is limited and is not capable of clamping castings and the like having only a short cylindrical part with corners and the like.
It is true that clamping arrangements for centering and clamping with mostly semi-circular clamping jaws with low surface pressures is known, these clamping jaws being adapted to the shape of the workpieces, as shown in German AS No. 2,212,055, but such devices require that the clamping jaws be shaped to adapt to the diameter of the workpiece being clamped which necessarily requires frequent adjustment when handling articles of different diameters.
It is also known to provide clamping arrangements for achieving lower specific clamping loads, such devices using tension bands partially encircling a workpiece in a cross sectional plane, examples of which are found in U.S. Pat. No. 3,661,378; British Pat. No. 860,754; and U.S. Pat. No. 1,644,755. However, a centrical clamping of round workpieces varying in diameters is not possible with these arrangements.